We have discovered that the pattern of temporal variability of spontaneous pain can be readily measured in clinical pain conditions, and that normal healthy subjects cannot mimic this variability. This pattern of variability was well characterized by measuring its fractal dimension 'D' of consecutive ratings of spontaneous pain. Our preliminary results suggest that D is different between chronic post herpetic neuropathy patients, chronic back pain patients, normal subjects imagining having back pain, and normal subjects rating a thermal painful stimulus. These observations suggest that temporal variability of spontaneous pain may be an objective measure of pain and may provide information regarding the dynamical processes in the nervous system. This proposal rigorously tests the latter claim in a larger population of chronic back pain patients. Specific aim 1 examines fractal properties of pain ratings in larger time windows. Specific aim 2 tests the variability of the fractal dimension and contrasts this variability with linear statistical measures, like the mean and standard deviation of present or average pain. Specific aim 3 examines the relationship between fractal properties and clinical characteristics of back pain. These experiments test the utility of measuring temporal dynamics of spontaneous pain as a new and objective tool regarding clinical pain conditions and examines the power of the technique in revealing insights regarding nervous system control mechanisms that modulate pain conditions. [unreadable] [unreadable] [unreadable]